There have been three major color correction methods. They are HSL method, RGB method, and BGC method.
Firstly, HSL method is a color correction method that is based on three properties of a color, Hue (H), Saturation (S) and Lightness (L), which corrects colors by interpreting them respectively.
Secondly, RGB method is a color correction method that was developed based on color space with color information, which is a method of controlling Red (R), Green (G), and Blue (B) independently.
Lastly, BGC method is a traditional color correction method that has been used for controlling color in TV CRT. It corrects colors by using Brightness (B), Gamma (G), and Contrast (C), which makes it possible for the user to control the color of CRT easily by referring to the meaning of the terms.
Referring to FIG. 21, explaining the BGC method in detail, BGC respectively stands for Brightness—Gamma—Contrast. That is, traditional method for controlling colors of TV CRT by which controls the dark-tone area, mid-tone area, and highlight area. It is a method by which controls the color in accordance of the ranges of tones. RGB Method can be explained as variation in axis of color space, which makes it different from BGC method. RGB Method can be explained as variation of value in space and BGC method as variation on a line.
Referring to FIG. 21, the difference between the two methods comes from the variation on a line, which is a diagonal line which appears on the right of the picture. The picture on the right side is a curve showing the input/output relation of histogram. The detailed explanation about histogram will be given in the later part of this specification.
In the input on X axis and output on Y axis, it becomes darker on left and down. Since it shows the input/output relation in gray gradation tone, it becomes a line. Consequently, input/output relation that depicted as diagonal line can be controlled to vary the output in relation to input so that color can be controlled. As mentioned, in accordance with the tone range, the shape of the diagonal line is controlled by using Brightness—Gamma—Contrast buttons, of which the functions are shown in FIG. 21.
Shape of the curve can be freely controlled by using B, G, and C buttons respectively in combined way. Consequently, users can control the relation of input and output to desired shape. First, controlling the Brightness will affect the entire output for input. And, by controlling the Gamma the shape of diagonal line will be controlled to be inflated shape to the upper or downward direction and intermediate brightness area can be controlled. Finally, controlling the Contrast will affect only the bright area. Consequently, Gamma controls intermediate brightness area, Contrast controls bright area and Brightness controls the entire area. However, even thought controlling the Brightness affects entire area, there are separate functions of controlling the other two areas, and it is used to affect only the dark area. In conclusion, BGC method can be understand as a method that induce relative change of the output to the input by varying the shape of the line representing the input and output relation.
In addition, for precise color correction, in traditional color correction method, it is divided into to Shadow (S), Mid-Tone (M) and Highlight (H) to control the areas respectively. In case that area to be corrected is not selected in accordance with the lightness, automatically entire areas (Master, M) can be applied.
Since Human visual perception does not respond each area evenly, it is more efficient to control the areas one by one in accordance with the lightness in the aspect of color correction. In this sense, color correction based on the respective area can be said to be necessary. Above mentioned can be summarized as shown in the table of FIG. 22.
On the other hand, advances in computer technology led to many changes in aspects of color correction of photographs and images. First, environment has been provided in which methods mentioned above can be used in a variety by a combination of a variety of ways in the actual computer environment. The environment was provided in which users can freely select any way, which is the way based on the properties of colors, the way to reproduce colors on a monitor, and the traditional way of CRT TV.
However, since the color reproduction in the computer environment was developed with a mouse-interface, the way of controlling the color correction has naturally devolved to limited to the principles and way to use the mouse.
Today, due to technological advances of new input devices, paradigm shift of the color correction interface that was used in the existing computer environment is required. In other words, the age of a paradigm shift has come from the mouse-way using the ‘one-click’ way to the ‘multi-touch’ way with a multiple input.
In this digital environment, there have been conventional color correction methods for images (photos and videos) and the following user interfaces. They are SLIDE BARS UI method, COLOR WHEELS UI method, COLOR PICKER UI method, CURVE UI method.
The above conventional color correction methods for images and the following user interfaces will be described with reference to the accompanying drawings.
SLIDE BARS UI Method
The SLIDE BARS UI method is a typical user interfaces method that has been used for correcting color of images and photos in a digital environment. As shown in FIG. 15, each slide-bar that work independently is adjusted to adjust Color (Hue), Saturation, and Brightness (Lightness) of HSL-way. At least three movements are needed to adjust the color on the actual operation. Also, it is inconvenient to verify the change of images (photos, video) comparing the degree adjusted by actual mouse with displayed images (photos, video).
COLOR WHEELS UI Method
COLOR WHEELS UI method is a method using a vector. Value of the vector is determined by the direction and distance thereof. In this method, the reference point which is the initial value of the color wheel is moved to a specific location, thus direction and distance thereof is changed, and the value of newly changed colors is created.
The property of colors is controlled through the color wheel, the color (Hue) is determined by the moving direction, and the Saturation is determined by the moved distance. FIG. 16 illustrates a typical color wheel. The figure on the left shows the appearance of the initial value before its change and the figure on the right shows the appearance in case of moving the center point to change colors and saturations.
In this method, although it is possible to adjust the two properties (color (hue) and saturation) through one movement, it is not possible to adjust the three properties (color (hue), saturation, and brightness) which are needed to adjusted to correct colors all at once.
There are all three properties of the color, thus another movement is required for remaining one element. In other words, there is a problem that the vertical bar on the screen on the most right side representing the brightness still did not change and vertical bars is controlled by separate actions. FIG. 16 shows that the vertical bar on the screen on the most right side representing the brightness still does not change.
COLOR PICKER UI Method
Referring to FIG. 17, COLOR PICKER UI method is a method for picking colors. In the other words, users select the wanted color directly on the screen in this method. For more sophisticated color choices, it is possible to input detailed values with numerical values.
The function of the COLOR PICKER UI method is different from that of the method described above, and it is similar to the function for selecting a color when users draw a picture rather than the function for regulating the color. Therefore, it is not frequently used in color correction tools for actual images.
One of the advantages of the color picker is that can be used by changing several modes. In FIG. 17 of the right-hand side of the screen, several radio buttons that looks like go-stone are shown, and these buttons have the function mentioned above. For example, when the user want to select a way (function) relating the color (Hue) in the color properties, it is possible to select the radio button ‘H’. Then, the color picker window of the square shape in the left side is changed to a color mode. Explaining the method for selecting in detail, the radio button ‘H’ (Hue, color) is selected, and the window is changed to the color mode. Then, a vertical bar located in the middle of the screen is adjusted to select desired colors in the color spectrum. Therefore, the corresponding color is displayed on the left side of the screen and the desired saturation (S) and brightness (L) of the color can be selected by clicking them on the screen. The corresponding saturation (S) and brightness (L) is selected based on the color.
Referring to FIG. 17 at the upper side, RGB, CMYK, or Lab select buttons in addition to H, S and B appear among radio buttons at the right side. Described through the following Figure, each concept is more easily understood. For example of a typical RGB color space, more related content will be described in detail. FIG. 17 at the bottom side shows the RGB color space. In the digital environment, all colors is reproduced by numerical values, and these numerical values will have a range of three-dimensional space, such as the FIG. 18.
Each of RGB or Lab will form three-dimensional space with axis of each of R, G and B or L, a, and b. The colors of the photos or images in this space will exist with one color coordinate value. In the Color Picker method, one of the radio buttons represent one axis, it is able to adjust other factors based on the axis. Thus, 3D three-dimensional color space is used in the space of a 2D two-dimensional plane.
However, in the color picker method, it is necessary to select a wanted color every time, and then re-adjust its value. This method is not different from the above mentioned method in that the user clicks multiple times and seeks the corrected color, and has the same problem.
4. CURVE UI Method
CURVE UI method is not naturally made for the purpose of color correction. When the first TV CRT was invented, it has a problem of a poor quality. Thus, this function was provided in order to encourage a better quality for users to adjust the screen to suit their environment.
The concept of the curve is easily explained through FIG. 19. One of the images reproduced on a computer monitor as well as a TV CRT appears as shown in FIG. 19.
However, all CURVE UI methods need several points added for the fine-tuning of colors. Thus, in the end, it is necessary to click multiple times for adjustment in common with above-mentioned methods in terms of the user interface. A black image that looks like ridge will show in the middle of FIG. 19. This is the classified amount of physical data recorded on one image according to the brightness.
The concept is a little difficult to understand. For examples, try to imagine one black-and-white photo recorded as a file on your computer. The bright, dark and mid-tone areas of the black-and-white photo existed as files are recorded as digital numerical value. In the photo, the darkest area has a value of 0, the brightest area has a value of 255, and the mid-tone area has a value of roughly 127.
It does not matter whether the value itself is high or low. The brightness thereof is regulated as a numerical value (in case of 8-bit images) merely. Thus, the brightness information of the photo is displayed as black-and-white tone from the left side with zero (0) to the right side with 255.
The each brightness information of a photo image exists as a pixel, and the total amount of the distribution thereof is displayed by the bar graph according to the already qualified gradation (tone, brightness) from 0 to 255. As a result, because the vertical Y-axis on the screen represents the total sum of pixels with the same brightness distributed in one image and the horizontal X-axis represents defined brightness levels, the bar graph appears continuously.
In case of color photos, the three R, G, B channels are displayed as each with a gray tone, they are shown overlapped with each other on the one united screen. So, it becomes the same type of FIG. 19, same as a single channel of the black-and-white photo. The one displayed in this way is generally referred to as ‘histogram’ in a technical term.
The reason describing histogram is that the curve method is a method to correct the color by the amount of the distribution in brightness (tone) of each pixel indicated in the histogram. In other words, it is a method to display the amount of physical information of the histogram as output relationship to input. The X-axis of the curve is a input histogram information, and the Y-axis of the curve is a output histogram information. The color correction by the curve is a method to change this relationship.
FIG. 19 shows the typical appearance of the curve method. Bars with gray tone can be seen at the side of X-axis and Y-axis. As discussed above, because the X-axis is a input histogram information and the Y-axis is a output information, each axis shows with gray tone.
Because the curve method is same as that of histogram, the left area is dark and the area becomes brighter going toward the right side. Also the left side of FIG. 19 shows a one-to-one linear relationship of the input and output. In the right side of FIG. 19, the output information to the input changes. When the control points as shown in FIG. 19 are added, the relationship is able to change. In the curve method, there is a curve method to adjust the curve as a horizontal line as shown below in FIG. 20 as well as a diagonal line.
Likewise, the conventional color correction methods or interfaces were guaranteed for the accuracy and precision because they are used for a long period of time.
However, it is difficult to perform the method with the high accuracy and precision because the modern computer becomes smaller and lighter.
Instead, in a small display screen being easy to carry, the traditional color correction method used to improve the accuracy and precision can be more uncomfortable. Of course, differently from the method that was based on single touch with the click of a mouse, today's many devices are made for multi-touch recognition. These changes strengthen its inHuence rapidly like trends. In other words, the new age of a paradigm shift for the input device has come.
Thus, unlike the conventional method based on the single touch of keypad or touch-pad, there is a strong demand for the development of a new color correction methods or interfaces which can reduce unnecessary repetition of user's movements and enable color correction using user's intuition and one continuous movement in a device based on multi-touch function.